Physical and Sensing Properties of Aluminum-Doped Iron (III) Oxide Thin Films Deposited via Chemical Spray Pyrolysis

Abstract

Fe₂O₃:Al (1–3 at%) thin films were successfully grown on glass substrates at 400°C using the chemical spray pyrolysis (CSP) technique. The X-ray diffraction (XRD) patterns confirmed the formation of α-Fe₂O₃ with a prominent (104) peak, indicating high crystallinity. The average grain size (D) increased from 15.82 nm to 18.70 nm with increasing Al content, while the lattice strain (ε) decreased from 2.18 to 1.85, suggesting improved crystal quality. Atomic Force Microscopy (AFM) analysis showed a reduction in surface roughness and uniform particle distribution, with particle diameters ranging from 65.5 nm to 52.31 nm. Optical studies revealed a gradual narrowing of the bandgap values from 2.81 eV (undoped) to 2.74 eV, 2.69 eV, and 2.64 eV for 0 at%, 1 at%, and 3 at% Al-doping levels, respectively. Furthermore, gas sensing tests demonstrated that higher Al doping increased resistance and reduced sensitivity toward NO₂ gas due to enhanced charge carrier recombination and altered surface interactions, indicating significant influence on semiconductor gas sensing properties.